February 9, 2017
Expert opinion on using concrete for anvils or as anvil fill seems uniform that concrete is a poor material for anvil use due to its lower mass compared to steel and its vulnerability to fragmentation under repeated impacts. Given the fact that anvil costs are a big part of DIY power hammers, I would like some experienced opinion from others on this alternative:
Sand and gravel both can be compacted a great deal. Pea gravel on the other hand has zero compactabilty when merely dumped, but it is relatively cheap by weight. Could a concrete mix, with a very high portion of pea gravel rather than gravel, be used as fill to increase anvil mass? Yes a tube (if used) would have to be capped with a thick layer of steel, and the total volume would be greater than a steel anvil. But either poured in a form or used to fill a tube, pea-crete might enable more people to build hammers when obtaining the anvil mass is their major holdback.
I note that the Costa Rica anvil uses a part concrete anvil and that it is much smaller in volume than what you find below.
Comparatives; steel at about 490#/cubic foot. Assume a top steel cap of (say) 20#+ would be added.
Concrete ~150#/cubic ft, or about 30% that of steel.
At 10:1, an anvil for a 50# hammer would be 500#, and a 100# heavy steel tube filled with pea-crete would have to be increase by about 3 times the total volume of a solid steel anvil.
Some comparisons, all using 100# for the steel tube (form) weight:
A 100# 36” long x 10” diameter steel tube would contain 1131 cubic inches or 2/3 of a cubic foot, or 98# of concrete.
A 100# x 36”L x 12” dia steel tube would contain 1357 cu in or 78% of 150 or 117#.
A 100# 16” steel dia tube contains 1809 or 105% of 150# or 157#.
A 100# 24” dia tube 36 L would weigh….235#.
The above show that anvil size (at 10:1) would get quite a bit larger than solid steel.
What do you think?
April 26, 2010
The ten-to-one “rule” is not really a rule. There’s an engineering/science graph with a curve showing ratio versus efficiency. The curve rises steadily until about 90% at 10:1 and then flattens out. If there’s a “rule” it should be “don’t bother with an anvil heavier than ten times the hammer.
Again, it’s just a knee on a graph – it doesn’t account for how well/poorly things are attached to the ground or what the ground is made of or any other factor.
I would use steel. I wouldn’t want the energy from the tup to be absorbed (transformed to heat). I would want it reflected back upward into the work.Gravel doesn’t ring. Steel does.
No matter where you go... there you are.
February 25, 2012
Sorry I’m chiming in with neither the experienced opinion from building hammers that you are seeking nor as much background in engineering as Lee has. What I do have is an Iron Kiss Octagon 75# pneumatic hammer that I acquired several years ago from Grant Sarver’s estate after he passed. There is pretty much universal agreement that the Iron Kiss hammers move a lot of metal quickly, hitting very hard for their tup (hammer) weight. They have a 20:1 anvil to hammer ratio. Yes, that means my hammer has a 1500# block of solid steel for an anvil!
Here’s a quote from Grant: “I think john’s hammers are the best hammers in their size – period! They hit with incredible force for their size and don’t require anything additional in the way of base or even foundation due to their very heavy construction and 20:1 anvils.”
So I’m kinda questioning the advice to not bother with more than a 10:1 ratio. Sure, there could be other explanations for why the Iron Kisses hit hard; perhaps the hammer moves with greater than average velocity, or perhaps it is the heavy duty construction of the frame. But James is correct about the anvil being a big part of the cost of building a hammer, and I doubt John Larson would have added so much to the price of his line of hammers without a very good reason.
I do however totally agree with the advice to choose steel over concrete. I would focus on finding a cheap source of steel. Weld a bunch of scrap plate together. Or maybe you could fill your tube with used ball bearings scrounged from machine shops? (you know, pea gravel on steroids!)
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